Hydrophobic reagents, such as the alkylureas and the Hofmeister series of salts have been used to probe the contact areas subunit proteins. The dissociation is studied by effects of any given reagent on the molecular weight using conventional and laser light scattering methods. In the case of horse and human hemoglobin, analysis of the dissociation data obtained with urea and guanidinium chloride give estimates of 16 to 20 amino acids that become exposed at the alpha1 beta2 contact areas as the protein tetramers dissociate to dimers. The analysis of the dissociation data also affords estimates of the fractional accessibility, mean alpha of the amino acids at these areas of subunit contacts. Estimates of mean alpha of 0.28 and 0.24 were obtained with the horse and human hemoglobins that compare favorably with the corresponding estimates of 0.29 and 0.26 based on X-ray crystallographic information, reported by Chotia and coworkers. The dissociation behavior of the dodecameric and hexameric component of crab hemocyanin was also investigated using the alkylureas and salts as dissociating agents. The ureas were found to be increasingly more ineffective as dissociating agents with increasing hydrocarbon content of the reagent, suggesting that hydrophobic effects are not the major stabilizing interactions that hold together the hemocyanin subunit. Light scattering studies are also in progress on other subunit proteins.